Systémy, které kombinují kvantové a klasické stupně volnosti v nerovnováze
| Thesis title in Czech: | Systémy, které kombinují kvantové a klasické stupně volnosti v nerovnováze |
|---|---|
| Thesis title in English: | Quantum-classical systems out-of-equilibrium |
| Key words: | nerovnováha|spinová dynamika|transport |
| English key words: | nonequlibrium|spin dynamics|transport |
| Academic year of topic announcement: | 2023/2024 |
| Thesis type: | dissertation |
| Thesis language: | čeština |
| Department: | Department of Condensed Matter Physics (32-KFKL) |
| Supervisor: | RNDr. Martin Žonda, Ph.D. |
| Author: | hidden - assigned and confirmed by the Study Dept. |
| Date of registration: | 25.01.2024 |
| Date of assignment: | 25.01.2024 |
| Confirmed by Study dept. on: | 12.02.2024 |
| Advisors: | RNDr. Pavel Baláž, Ph.D. |
| Guidelines |
| The main initial goal for the student will be to implement a method based on a quantum-classical approach, that allows to calculate non-equilibrium transport through a system, where the correlations between the electrons play a significant role. This is a common situation for various experimental setups including different devices relevant for molecular electronics and molecular spintronics. We will apply this method to address such systems. Next challenge for the student will be to develop a method suitable for the investigation of non-equilibrium dynamics of a correlated system coupled to superconducting leads. This is relevant for the investigation and manipulation of the so-called Yu-Shiba-Rusinov states or Andreev bound states which play a crucial role in phenomena like quantum phase transitions and might be relevant for building gates in future quantum computers. |
| References |
| [1] R. Smorka, P. Baláž, M. Thoss, M. Žonda, Nonequilibrium dynamics in a spin valve with non
collinear magnetizatio, Phys. Rev. B 106, 144435 (2022) [2] R. Smorka, M. Žonda, M. Thoss Electronic transport through correlated electron systems with nonhomogeneous charge orderings, Phys. Rev. B 101, 155116 (2020) [3] P. Mondal, A. Suresh, and B.K. Nikolić, When can localized spins interacting with conduction electrons in ferro or antiferromagnets be described classically via the LandauLifshitz equation: Transition from quantum manybody entangled to quantumclassical nonequilibrium states, Phys. Rev. B 104, 214401 (2021) [4] P. W. Anderson, More is Different, Science |
| Preliminary scope of work in English |
| The physics of condensed matter is full of open problems with a huge number of interacting constituents that one must deal with. That is, in general, a hard problem becoming unsolvable if quantum description is necessary. There are many strategies for how to address it. In some cases, one can construct a classical approximation which is then used to simulate large systems. However, this is not always an option, as the property in question might not have a classical analogy at all. On the other hand, a full quantum mechanical description can be often effectively applied only on small systems of few constituents. Here the issue is that more is different, even an exact solution of a small system might not capture the physics of the large one.
In many scenarios a compromise can be utilized, namely, a hybrid method that combines classical and quantum degrees of freedom. Here one takes slow, heavy or “continuous enough” degrees of freedom and approximates them by classical dynamics. The rest of the system is treated quantum-mechanically. For example, in the case of magnetic systems these methods consider classical localized magnetic moments interacting with quantum conduction electrons. For correlated electron systems, we can use classical fluctuations to describe the correlations between the electrons beyond mean-field approximation. In this way, one can use quantum mechanics where it is necessary and classical dynamics where the enormous size of the system plays a crucial role. |